Sunday, September 29, 2013

Nearly every traffic engineer that has a shred of experience with research knows about Webster and the concept of an "optimal" cycle length at signalized intersections. The research completed by Webster is almost 50 years old yet the traffic signal timing tools that we use continue to use these days are based on these traditional methods. As I am reviewing the 2nd Edition of the Signal Timing Manual as the Chair of the National Cooperative Highway Research Program (NCHRP) project, I was very pleased to see this thoughtful text by the authors (lead by colleagues at Kittelson & Associates, Inc.)

critical intersection methods use Webster’s model to determine optimal cycle length, which has a de facto outcome focused on vehicle flow, not specifically considering the needs of other users, such as pedestrians, bicycles, and transit.

Bicycle traffic in downtown Portland (after a bridge lift)

There has been some work by my colleagues at the Texas Transportation Institute focused on the newer versions of the Highway Capacity Manual that focus on updating the 50 year old research and while that's good, the point of this post is to focus on the importance of policy. Policies should be carefully consulted in a cycle length selection process. The Signal Timing Manual, First Edition, highlights that in Chapter 2. Originally, that Chapter was met with some dismissive comments from the Panel of experts reviewing it. One professional cited too much use of the term "priority" meaning they didn't want transit to get special treatment.

A community with a emphasis on multimodal transportation should select cycle lengths that respond to the needs specific to the intersection. Lower cycle lengths are better for multimodal transportation in general. Lower cycle lengths are also best with shorter block lengths because of the potential for longer periods of red to stack traffic up between signals. Downtown Portland has both the policy and the aforementioned physical attributes (I originally wrote constraint but corrected myself because many consider this an asset) , that necessitate a very short range of cycle lengths: 48- (midday), 56- (a.m. peak), or 60-seconds (p.m. peak). These short cycle lengths provide quick changes for pedestrians.

Pedestrians in a downtown environment benefit from short cycle lengths In Portland, there's progression for pedestrians too, but that's another post.

and limited progression for buses that stop every two, three, or four blocks.

The progression speeds that follow from the short cycle length are slow to promote a safe environment for people on bicycles to take the lane and feel comfortable doing so.

Monday, September 23, 2013

I described my day job as traffic signals engineer and my volunteer night position as flyer producer for worthy causes like #walknbike day October 9th! Get excited and join me in getting the kids in the neighborhood to school in a multimodal fashion. I don't make flyers very often, but it was fun to think about how to share a message about something that used to be a very normal thing to do, but now has to be something that we take a day to make a big deal about and distinguish as a particular day that we walk & bike.

At the traffic signal immediately adjacent to our hotel, I sat and watched traffic for several hours marvelling at the range of vehicles, the behavior of travellers, and the integration of modes. My observations left me a little uncomfortable because pedestrians were often forced to yield to vehicles that were asserting their "right" to move in front of a legal movement.
The range of age of people at the intersection was also interesting, some of the people at the intersection that were the slowest seemed the most comfortable making movements that would make a traffic engineer like me cringe.

These photos are enjoyable because they represent just a few of the cargo bikes mixing with buses, heavy trucks, and passenger cars in the intersection.

Tuesday, September 17, 2013

I did not make up the acronym, I have to attribute that to my colleague, but here's a post on a new warning device in downtown Portland.

This "Bus Only Activated Transit Sign" (BATS) was activated by the City in cooperation with TriMet at their request. The intent of the sign is to warn pedestrians traveling in the east-west direction on Burnside of a bus approaching from the left turn (westbound direction). The warning sign is a caution indication designed to support the pedestrian indication as this is an area where TriMet has complained of a considerable amount of people walking in front of their left turning bus when they have a Don't WALK indication. Part of the "problem" in downtown is that there it is mostly just two phase intersections, so a left turn crossing maneuver is a bit of an anomaly. in most intersections, there isn't the expectation that this left turn conflict will be experienced and this one is particularly intermittent since it is a bus only movement and it only is active if a bus is present.

I have been invited to share some perspective on traffic signal operations for the Street Design Guide.

TRB 2014 Workshop on NACTO Urban Street
Design Guide

Sunday,
January 12, 2014

9:00am –
12:00pm

Hilton
Hotel

Summary

NACTO’s
Urban Street Design Guide charts the principles and practices of the nation’s
foremost engineers, planners, and designers working in cities today. A
blueprint for the 21st century street, the guide offers an inside perspective
into how cities can transform their streets to confront the demands and
challenges of the near future. From public plazas to BRT to stormwater
management, the guide provides an in-depth overview of how to design livable,
multimodal, and resilient city streets.

Topics:

9:00-9:20 Introduction
andOverview of Urban Street Design
Guide

Speaker: David
Vega-Barachowitz, NACTO

[David will add something re. his presentation]

9:20-10:00 Complete
Streets Across Different Street Types

Mike Flynn, NYCDOT

In an urban context, street design must meet the needs
of people walking, driving, cycling, and taking transit - all in a constrained
space. Mike Flynn will draw on NYCDOT’s experience in designing complete
streets for different sizes and contexts.

10:00-10:10 Break

10:15-10:35 Intersection
Design Principles

Michael King,
Nelson/Nygaard

As focal points of activity for pedestrians, drivers,
and cyclists, intersections are a critical part of the city streetscape and
transportation network. Good intersection design maximizes visibility and
creates a safe and intuitive space for people driving, walking and cycling,
promoting economic growth and active street life.

The use of interim materials gives cities greater
flexibility when making changes to the streetscape by enabling projects to be
implemented in the short term, allowing the community to weigh in on the
space’s effectiveness before creating the permanent condition. Examples
of interim materials use are plazas and parklets, pedestrianizing a corridor,
or redesigning complex intersections.

10:55-11:05 Break

11:10-11:30 Signalization
Strategies:

Peter Koonce,
Portland

The allocation of time by
traffic signals is as important as the allocation of space in governing how
streets operate. Signal timing tools such as Leading Pedestrian Intervals and
Split-Phasing can help ensure safe environments that support walking,
bicycling, public transportation, and economic vitality.